1. Field of Invention
The present invention relates to the semiconductor field, and specifically to a three-dimensional thermoelectric energy harvester and a fabrication method thereof.
2. Description of Related Art
With the development of the Internet of Things, its applications in the industrial, commercial, medical, consumption and military fields are gradually expanded. Power source is always critical to prolonging the service life and reducing the cost of the Internet of Things. In environmental extremes or other occasions unreachable to human beings, or when a network node moves or changes, it is difficult or even impossible to replace a battery, making it crucial to effectively provide energy to a node of the Internet of Things. An effective solution is to harvest ambient energy through energy harvesting, store the energy and provide the energy to the node of the Internet of Things. Temperature difference is widely present in the external environment. Therefore, energy harvesting using the temperature difference in the environment has been extensively studied.
A vertical-type miniature thermoelectric energy harvester as shown in FIG. 1 is currently commonly used, because the direction of heat flow is perpendicular to the substrate, and the thermoelectric energy harvesting efficiency is high. Upper and lower substrates exchange heat with the external environment, and transfer an external temperature difference to a thermopile, and the thermopile converts the temperature difference in the external environment to a voltage signal by using the Seebeck effect and outputs the voltage signal, thereby harvesting external energy. Since thermocouples are arranged perpendicular to the substrate, a planar semiconductor process cannot be adopted, and instead, the thermocouples are generally fabricated by an electroplating or thin-film sputtering deposition process. Current vertical-type thermoelectric energy harvesting chips generally adopt a BiTe-based material or a metal material such as Cu or Ni as the thermoelectric material. Since the metal material such as Cu or Ni is a conductor structure having a small Seebeck coefficient, thermoelectric energy harvesting chips fabricated by using the metal material such as Cu or Ni as the thermoelectric material generally have low efficiency. Since the BiTe-based material is a semiconductor structure having a high Seebeck coefficient, thermoelectric energy harvesting chips fabricated by using the BiTe-based material generally have high efficiency. However, the BiTe-based material requires a high cost, and contains toxic substances, which limits the use of BiTe thermoelectric energy harvesting chips. In addition, since the composition of a thermocouple requires two thermoelectric materials, the vertical-type thermoelectric energy harvester generally needs to be subjected to two electroplating or thin-film sputtering deposition processes in order to fabricate a thermocouple material, which further increases the cost of the thermoelectric energy harvesting chip. Moreover, the fabrication efficiency of the vertical-type thermoelectric energy harvester is low, because the thermoelectric energy harvester is thermally and mechanically connected to the upper and lower substrates through chip-level bonding.
In view of the above reasons, it is necessary to provide a low-cost, high-efficiency thermoelectric energy harvester.